1. Field of the Invention
This invention relates to an observation apparatus for endoscopes which is suitable for observations on a tumor and the like in a human body, and in particular to an observation system for endoscopes including this apparatus.
2. Description of Related Art
The observation of a tumor requires the use of a particular drug which has properties of being easy to gather on a cancerous cell and of emitting fluorescent light by the irradiation of light. Specifically, the drug with such properties is made to penetrate an object to be observed by means of injection or spraying, and the object is irradiated with excitation light through an excitation filter which transmits components lying in a region of relatively short wavelengths, of light from a light source, so that fluorescent light emanates from a particular part of the object. This fluorescent light is introduced into a TV camera, through an observation filter which blocks the excitation light to transmit components in a region of relatively long wavelengths including fluorescence wavelengths, so that a fluorescent image is obtained.
In a conventional system of this type, the transmissive wavelength region of the excitation filter is independent of that of the observation filter and thus the fluorescent image is observed against a dark background. This situation obscures the relative relationship between the image of the object as seen with the unaided eye and the fluorescent image. Hence, a technique has been used that the image of the object is formed with visible light by using proper means, and this image (ordinary image) and the fluorescent image are displayed in parallel on a single TV monitor. The result is that the images are very hard to see in practice and this fact becomes a great burden to an observer.